The interfacial surface tension of cyclic olefin polymer (COP) and cyclic olefin copolymer (COC) microfluidic devices is relevant, for example, for droplet-based microfluidic applications in which aqueous droplets are manipulated within a perfluorinated or silicone based oil. The surface tension properties of materials can often be altered through the adjustment of surface chemistries. Unfortunately, the relative non-reactivity of the COP and COC substrates commonly used in microfluidic devices makes their surface modification difficult or in some cases impossible.
Previous efforts to improve microfluidic device surface tensions have focused on silane modification of the COP and COC substrates (Zhou (2010) Electrophoresis 31:2; Gandhiraman (2010) J. Mater. Chem. 20:4116; and Dudek (2009) Langmuir 25:11155). This approach was found to produce surfaces having inconsistent quality and performance, presumably because the silane was not covalently attached to the substrates. Instead, the silanes most likely pre-hydrolyse in solution, as a network polymer is physisorbed onto the COP/COC substrate.
A recent alternate technique for modifying the surface of COP and COC substrates involves UV-graft polymerization on monolith structures within microfluidic channels (U.S. Pat. No. 7,431,888). The use of a benzophenone photoinitiator in the presence of a solution phase of monomer allows COP and COC substrates to be covalently modified with a multitude of monomers of both acrylate and methacrylate functionality. These monomers could also be terminated with fluorophilic, hydrophobic, hydrophilic, and formally charged groups.